Fight Jade
To fight Jade, work your way to the match before the mystery fight (the one titled "?"). During this battle, defeat your opponent using nothing but low kicks. If you manage this feat you'll fight Jade in the next battle.

Pong
Get 250 fights (the number of battles at versus screen) and a message will appear transporting you to another dimension. Both players can now play Pong, who ever wins continues to play.